Overview of Optics and Lattice

1. Overview of Optics and Lattice Yunhai Cai For PEP-II Optics Task Force October 25, 2006 PEP-II Machine Advisory Committee Meeting

2. MAC recommendations • Develop a focused and schedule-oriented approach to achieving a high quality optics model and lattice correction capability. • Develop the machinery to allow rapid iteration between measurement and correction. • Aggressively pursue lattice correction in both rings to drive the actual lattices to the design. • Pursue model-based coupling analysis and correction.

3. Organizationwith Persis Drell and John Seeman • The website created by PT will be maintained by Walter (thanks) to include minutes, official decks, summary of all existing tools • Walter Wittmer is a special assistants for the group leader • First person listed in the task sheet is the leader for the task. He coordinates the task activities • All names on the task sheet are core members in the optics group and they should spend at least 50% to their time for the optics tasks • The group should have significant inputs to MD plan in order to effectively improve the specific luminosity. An integrated MD plan for optics should be carefully developed by the group leader. • MD goal, plan, and report are required • Reasons of the failure will be recorded as action items • The old method with possible improvements should be tried again • New ideas and methods are always have the highest priority • A task force meeting will be held by the group leader at 3:00 p.m. in Fuji room every Wednesday. It is opened to all and John Seeman and Uli Wienands will be invited.

4. Critical Tasks at the Moment • Improve online model (M. Woodley) • Robust MIA model (Y. Yan) • Reduced ORM model: (G. Yocky) • Stability of orbit (J.Turner) • Orthogonal IP knobs (W. Wittmer) • Correction schemes: high level applications (YC) • Vertical steps in LER (Pantaleo Raimondi?) • Damping wiggler configuration (YN&FJD, nearly done!) • Solenoid compensation (PR?, YY?) • Dynamic aperture near half integer (Y. Nosochkov) • Develop a fast and robust tuning procedure (FJD?)

5. Beta Beating Correction in the HERFeb. 16, 2006 • Reduce the beta beating in the HER from 250% to 15% • Predicted the correction with an accurate model using MIA and LEGO • Tweaked single quadrupole: QF5L by +0.225% • Moved closer to half integer nx=0.516 • Reduced coupling in the HER within several hours, compared with several days, using MIA • Reached specific luminosity of 4.0 • Tweak of skew quadrupoles for additional 15% gain

6. Prediction from Beam-Based Model Horizontal tune is fixed with tune trombones back to 0.516.

7. Comparison of Measured b Functions Actual tweak of QF5L was twice larger than predicted.

8. Chromatic Optics for the HERFeb. 16, 2006 • Measured chromatic optics and dynamic aperture in HER • Excellent agreement between measurements and LEGO model in the chromatic optics • Improvement of understanding of nonlinear dynamics including sextupoles J. Yocky, P. Raimondi

9. A Beam-Based Online Model Linux: PEP-II optics Optics codes MAD DIMAD LEGO AT Model codes MIA VAX: SCP database: R-Matrix Or Twiss steering package beta measurement buffer data To be completed by Woodley and Yan by February 28, 2006

10. Built Beam-Based Online Model for HER Within Four Hours (March 7, 2006, Mark Woodley and Yiton Yan) nx ny x-oscillation dispersions

11. Steering in LERMarch 9, 2006 J. Turner, J. Yocky, F.J. Decker, please note that the scaled was reduced by a factor of two.

12. Beta Beating and Coupling Correction After the Steering bx bx coupling coupling Before After

13. High Level Applications (LEGO) • Simulations have been carried out and some of them were tried manually in the LER in past year • They are all SVD based and good for small iterations • Applications: • Dispersion correction with anti-symmetric orbit bumps • Coupling correction with symmetric vertical orbit bumps • Beta beating correction with symmetric horizontal bumps • Beta beating correction with quadrupoles

14. Lattice Parameters for PEP-II

15. Beam-Beam Scan, 3/16/06

16. Beam-Beam ScanMeasurement (3/16/06) & Calculations Dynamic beta and emittance and hour-glass effect are not included. Dynamic beta and emittance and hour-glass effect are included.

17. Improvement of Specific Luminosityafter three MDsMarch 18, 2006 Luminosity Specific Luminosity The 1E34 cm-2s-1 luminosity was reached at October 10, 2005.

18. PEP-2 LER Dynamic Aperture Simulation • Single beam dynamic aperture versus tune and Dp/p. • Realistic MIA machine model, b* = 36 / 0.8 cm. • Tune space near half-integer is limited by resonances, especially 2nx – nns , and chromatic tune spread. • Best aperture at tunes .522 < nx < .530, ny > .574. • Better compensation of the 2nd order chromatic ny tune shift is needed. ny nx 2nx-2ns 2nx-ns Dp/p 2nx-2ns best aperture nx+ny-4ns nx+ny-3ns > 10s aperture at Dp/p = 0 Dp/p = 5s = .00355

19. Move Toward Half Integer Tune previous working point • Three-dimensional simulation using BBI • MIA models are used for the inputs • Simulation is carried out at currents of 1600mA/2400mA • Lower both x and y tunes to gain luminosity shown on a contour plot in unit of 1E33 cm-2s-1 We made a quantitative prediction and followed by: • MD study and identified beam-beam lifetime as the limitation • Run x-chromaticity -1 to improve chromatic optics • Tweaked SCY3 by 7% to gain beam-beam lifetime • Lower the VRF from 4.5 to 4.0 MV • Actual tune change was accomplished by operators during the delivery Y tune current working point LER x tune

20. Tune Shift along the Bunch TrainAlan Fisher horizontal vertical 0.0025

21. Summary of First Three Months, May 29, 2006 • Built fast and accurate online model • Developed correction schemes to correct beta beating and coupling in arcs • Reduce the amplitude of orbit in LER • Reduced the beta beating in both machine below to 20% • Developed a systematic and orthogonal procedure to correct optics after a major change of lattice • Nearly all milestones set by the end of March were reached • Most important, we worked at a term for a common goal

22. Status and Issues • Machine has developed large beta beatings after long running period without MD • Machine has to be regularly maintained • Since we moved to near half integer (nx=0.506), our beam-beam model did not agree with the machine and therefore lost its predictive power. • Optics is harder to model • Tune shift due to resistive wall • Limited man power: less than 4 FTE to cover both optics and beam-beam study • How to make correction applications avaible to everyone in the control room? • AIDA and a new hire in the control department

23. Members in Optics Group • Franz-Josef Decker, bump and correctors • Jerry Yocky, chromatic optics, BBA • Jim Turner, orbit steering • Kiran Sonnad, orbit stability • Mark Woodley, online model • Pantaleo Raimondi, beam dynamics • Uli Wienands, MD scheduling • Walter Wittmer, IP knobs • William Colocho, automate procedures • Yitan Yan, optics modeling and correction • Yuri Nosochkov, lattice design • Mike Sullivan, IR and beam-beam measurement

24. Future Improvements of Optics • 900 HER lattice to reduce the momentum compaction factor (It is being implemented) • Lower the by* 8 mm (20% luminosity gain) • Reduce the vertical emittance in the LER or make a design near the vertical bending region (15% luminosity gain) • Turn on wigglers to reduce the damping in the LER (5% luminosity gain)

25. Damping Wiggler Latticefor the LER without orbit bumps with orbit bumps • Lattice was designed by Franz-Josef Decker and Yuri Nosochkov. • Reduce the damping time by 15% and expected luminosity gain 5% at high beam currents. • Wigglers induce changes in orbit, optics (mostly in the vertical), and path length. • Lattice of wiggler was test in MD • Wiggler (80%) and its optics correction was good • But orbit did not work as expected, very poor beam lifetime

26. Conclusion • We have implemented many recommendations suggested by PEP-II MAC committee • Fast and accurate online models were built • Many correction schemes were developed and used in machine • Reliable beam-beam simulation to guide MD study • Both ring operated near half integer (nx=0.506) • Significantly increased the success rate of machine development • We have gained 15% luminosity from the optics work. But many challenges remain • Stability of machine • Accurate IP tuning knobs • Accurate beam-beam model near the half integer • Robust online model and correction programs